$300 labour to replace MAF??? you kidding me?

Unless C280 is significantly different from C220 the MAF should be located right in front of you when you open the hood and the part comes off with 2 clips and a hose clamp....

stealership these days....

Edit: nope it isn't any different from a C220:

you see that tube-like thingy next to the coolant reservoir bottle with a cable connected to it?

yup that's the one.